Search

The nuclear heat loads due to gamma rays emitted from the decay of 16N and delayed neutrons from17N, generated by the activation of water in cooling circuits, are critical for ITER design. The assessment of nuclear heating from activated water is complex; it requires temporal and spatial dependent transport and activation calculations taking into account variation of irradiation, water flow conditions and cooling circuits’ parameters. A water activation experiment has been recently conducted at the14 MeV Frascati Neutron Generator (FNG) in order to validate the methodology for water activation assessment used for ITER and to reduce the safety factors applied to the calculation results, which have a large impact on the schedule, commissioning and licensing. Water circulating inside an ITER First Wall (FW) mock-up was irradiated with 14 MeV neutrons and then measured using a large CsI scintillator detector. The system consists of a closed water loop where the cooling water, transiting through an ITER FW mock-up, is irradiated by FNG. The induced 16N activity via 14 MeV neutrons interactions with 16O via the 16O(n,p)16N reaction is measured in a dedicated counting station via an expansion volume. The water then passes to a much larger holding delay tank, and after several 16N half-lives decay time, it is then recirculated and exposed again to neutrons in the ITER First Wall (FW) mock-up. The measured 16N activity is obtained measuring the emitted characteristic 6.13 and 7.12 MeV gamma-rays. Calculations were performed in an accurate model of the FW mock-up using the MCNP Monte Carlo code and FENDL-3.1 nuclear data library to obtain the predicted flux impinging on the water. The EASY-2007 inventory code was used to predict the 16N activity. In this work, a comparison between measurements and calculations is reported together with associated uncertainty analysis.

The Water Cooled Lithium Lead (WCLL) is one of the breeding blanket (BB) concept candidate for the future European Demonstration Fusion Power Reactor (DEMO). In the frame of the EUROfusion Consortium, a WCLL BB mock-up neutronics experiment will be performed at the 14 MeV Frascati Neutron Generator (FNG) irradiation facility, devoted to the validation of the Tritium Breeding Ratio (TBR) and the shielding capability predicted by neutronics design calculations. It will include the assessment of the uncertainties on the calculated Tritium Production Rate (TPR) and the neutron/gamma attenuation which will be useful to evaluate design margins required to guarantee tritium self-sufficiency. In preparation of the future experiment, a detailed pre-analysis has been performed with the MCNP Monte Carlo code for the definition of the mock-up assembly and for the optimisation of the experimental setup. The WCLL mock-up has been designed in such a way that the essential nuclear features of the WCLL BB in DEMO can be represented in the experiment and the relevant nuclear quantities can be measurable with sufficient accuracy under FNG irradiation conditions, with several experimental techniques. This study reports the results of the pre-analysis: the optimised experimental layout and its representativeness of WCLL DEMO blanket.

Water activated by 14 MeV neutrons emits both high energy gammas from 16N and delayed neutrons from 17N. The isotopes 16,17N are produced through the 16O(n,p)16N (T1/2 = 7.13 s) and 17O(n,p)17N (T1/2 = 4.1 s) reactions, respectively. These sources of radiation represent one of the main issues for ITER having large impact on the design of the machine and on the qualification of components. To validate the calculation methodology used for ITER and to reduce the safety factors applied to the calculation results a water activation experiment was commissioned by F4E to ENEA and performed at the 14 MeV Frascati neutron generator (FNG). The experimental set-up consisted of a closed water loop, about 40 m long, where the cooling water, while transiting through an ITER FW mock-up, was irradiated by the D-T neutrons produced at FNG. 6.73 MeV gamma-rays from 16N and delayed (fast) neutrons from 17N were measured using a large CsI gamma-ray detector and an array of absolutely calibrated 3He detectors, respectively. This paper reports on the measurements of the delayed neutrons emission from 17N. The calibration of the 3He detector array and the experimental set-up are first discussed. Then the experimental results (E) for the delayed neutrons as well as the comparison with the calculation (C) performed using the MCNP Monte Carlo code (coupled to the FENDL3.1 data library) and the EASY-2007 inventory code are presented. The C/E ratio results close to unity, however it is affected by a very large error (> ±60 %) to be ascribed mainly to the uncertainty on the nuclear data used for calculation.

Single Crystal Diamonds (sCD) have been selected as neutron detectors for the ITER Radial Neutron Camera (RNC). This paper investigates experimentally the hardness of these detectors to 14 MeV neutrons in order to have indications of their limits of applicability in the RNC. The experiment has been performed at the Frascati Neutron Generator (FNG) facility using three sCDs of different thickness ( 500 , 300 , 100 μ m ). The degradation of the sCD Charge Collection Efficiency (CCE) with increasing 14 MeV neutron fluence has been found to be lower with decreasing sCD thickness. Strong polarization effects produced by the trapping of charge carriers in the defects produced by the neutron irradiation are observed already at about 4 ⋅ 1 0 14 n ∕ cm 2 in the 100 μ m thick sCD. A software correction of the polarization effect is proposed, which enables to extend the sCD range of operation up to higher fluences. Taking into account such correction, a 50 μ m thick sCD is expected to reach 1 0 15 n ∕ cm 2 with a CCE greater than 0.7.

A neutronics benchmark experiment on a pure Copper block (dimensions 60 × 70 × 60 cm3), aimed at testing and validating the recent nuclear data libraries for fusion applications, was performed at the 14-MeV Frascati Neutron Generator (FNG) as part of a F4E specific grant (F4E_FPA-395_01) assigned to the European Consortium on Nuclear Data and Experimental Techniques. The relevant neutronics quantities (e.g., reaction rates, neutron flux spectra, doses, etc.) were measured using different experimental techniques and the results were compared to the calculated quantities using fusion relevant nuclear data libraries. This paper focuses on the analyses carried-out by ENEA through the activation foils techniques. 197Au(n,γ)198Au, 186W(n,γ)187W, 115In(n,n′)115In, 58Ni(n,p)58Co, 27Al(n,α)24Na, 93Nb(n,2n)92Nbm activation reactions were used. The foils were placed at eight different positions along the Cu block and irradiated with 14 MeV neutrons. Activation measurements were performed by means of High Purity Germanium (HPGe) detector. Detailed simulation of the experiment was carried-out using MCNP5 Monte Carlo code and the European JEFF-3.1.1 and 3.2 nuclear cross-sections data files for neutron transport and IRDFF_v1.05 library for the reaction rates in activation foils. The calculated reaction rates (C) were compared to the experimental quantities (E) and the C/E ratio with relative uncertainties was assessed.

One relevant experiment selected for the DT phase at JET is the irradiation of the HCPB-TBM mock-up of ITER which will be located in front of the horizontal port of Octant-8. The neutronics performances of the HCPB-TBM will be studied through independent measurement techniques and the experimental quantities compared to the results of Monte Carlo simulation. Of paramount importance is the measurement of the tritium production rate (TPR) to be performed by using a single crystal diamond detector covered with a thin layer of 6LiF (LiDia detector). This requires the knowledge of the 6Li mass. In this work the 6Li mass calibration of the selected LiDia detector was first performed in a well characterized thermal neutron flux spectrum. Furthermore, a performance test of the detector was carried out by locating it inside a polyethylene phantom irradiated with 14 MeV neutrons at the Frascati Neutron generator. The experimental set-up was accurately simulated by using the MCNP5 code and the TPR compared to the measured one. The goal was to point out and assess the issues with the measurement method.

In this work we present the response of a new large volume 4H Silicon Carbide (SiC) detector to 14 MeV neutrons. The device has an active thickness of 100 μ m (obtained by epitaxial growing) and an active area of 25 mm2. Tests were conducted at the ENEA-Frascati Neutron Generator facility by using 14.1 MeV neutrons. The SiC detector performance was compared to that of Single-Crystal Diamond (SCD) detectors. The SiC response function was successfully measured and revealed a very complex structure due to the presence in the detector of both Silicon and Carbon atoms. Nevertheless, the flexibility in the SiC manufacturing and the new achievements in terms of relatively large areas (up 1x1 cm2) and a wide range of thicknesses makes them an interesting alternative to diamond detectors in environments where limited space and high neutron fluxes are an issue, i.e. modern neutron cameras or in-vessel tokamak measurements for the new generation fusion machines such as ITER. The absence of instabilities during neutron irradiation and the capability to withstand high neutron fluences and to follow the neutron yield suggest a straightforward use of these detectors as a neutron diagnostics.

Water activated by fast neutrons emits both high energy gammas from 16N and delayed neutrons from 17N. The radioisotopes 16,17 N are produced through the 16O(n,p)16N and 17O(n,p)17N reactions (thresholds about 10 MeV) and decay through the reactions 16N ( T 1∕2 = 7 . 13 ± 2 s) → 16 O + γ (67% @ 6.13 MeV, 5% @ 7.12 MeV) and 17N ( T 1∕2 = 4 . 173 ± 4 s) → 17 O → 16 O + n (37.7% @ 0.386 MeV, 0.6% @ 0.886 MeV, 49.8% @ 1.16 MeV, 6.9% @ 1.69 MeV), γ (3.7% @ 0.87 MeV), respectively. Activated water, flowing throughout a nuclear plant distributes the radioactivity to many critical components where personnel and/or instrumentation can be located thus depositing additional radiation dose which requires a proper shielding. This source of radiation represents an issue for a D-T fusion device like ITER which uses water as the main cooling fluid for components such as e.g. first wall and divertor. Owing to the scarce experimental information available for the cross sections of the 16O(n,p)16N and 17O(n,p)17N reactions and few benchmark validations, large uncertainties are affecting the calculations of the water activation induced by DT neutrons in a tokamak. In the attempt to improve the available nuclear data Fusion for Energy (F4E) tasked ENEA to carry on a benchmark experiment to validate the water activation calculations presently performed for ITER. This benchmark experiment was carried out in the year 2019 irradiating with the 14 MeV neutrons produced by the Frascati Neutron generator (FNG) a small size ITER First Wall mock-up. Demineralized water was circulating inside the mock-up and downstream of the irradiation zone the 16N gamma-rays decay and the 17N neutrons decay were measured using proper detectors. The experiment was simulated using the MCNP and the FISPACT codes. The obtained C/E values are in a range close to unit for both 16,17 N isotopes. However, due to the large uncertainty on the 16O(n,p)16N and 17O(n,p)17N reactions cross-sections, for some of the used cross-section data base, e.g. ENDF/B-VIII.0, the C/E is affected by large uncertainty. This is especially true for the case of 17N which production cross-section is affected by ± 60% uncertainty. In the attempt to measure and validate the cross-section data for 16,17 N production, the water activation experiment was repeated at FNG so to measure directly the 16,17 O(n,p) 16,17 N reaction cross-sections at almost monochromatic energies. The results of this new experiment are presented in this paper and compared to the data currently used by ITER project for calculating the water activation.

The 14 MeV Frascati Neutron Generator (FNG), designed and built at the ENEA Frascati research center, is a highly versatile active source of fast neutrons for research activities. Neutron generation at the FNG is based on the T(d,n)α fusion reaction, to produce 14 MeV neutrons with a flux up to 1×1011 neutrons/s in steady state or pulse mode. FNG can also produce 2.5 MeV neutrons via the D(d,n)3He fusion reaction.

In the present paper, the performances of single crystal diamond detectors "ad hoc" designed to operate at high temperature are reported. The detectors were realized using commercial CVD single crystal diamond films, 500 micron thick with metal contacts deposited by sputtering method on each side. The new detector layout is based upon mechanical contacts between the diamond film and the electric ground. The detector was first characterized by measuring the leakage current as function of temperature and applied biasing voltage (I-V characteristics). The results obtained using two different metal contacts, Pt and Ag respectively, while irradiated with 14 MeV neutrons at the Frascati neutron generator (FNG) are reported and compared. It is shown that diamond detectors with Ag metal contacts can be properly operated in spectrometric mode up to 240°C with energy resolution (FWHM) of about 3.5%. © 2016 IOP Publishing Ltd and Sissa Medialab srl.

A Mock-up of the inboard shield of the ITER International nuclear fusion reactor was realized at the Frascati Neutron Generator (FNG) at ENEA Frascati with the scope to measure the nuclear heating (total dose) in the superconducting coils. High sensitivity MCP-6 and MCP-7 dosimeters were used to measure the low (

The Frascati Neutron Generator (FNG) started operations in November 1992 making available to EU fusion community 14 MeV neutrons at an emission rate of 1011 s-1. The fusion community strongly supported the idea of international collaboration in neutronics experiments, data base and code improvement, development of (new) experimental techniques and detectors. FNG was designed and built in ENEA that also operates the machine at its own expenses. FNG is extensively used to perform benchmarks or mock-up experiments of interest to Fusion neutronics in turn validating nuclear data and codes. A number of activities in different fields within a series of collaborations are carried out at FNG so far.

A neutronics experiment performed at the Frascati Neutron Generator (FNG) on a mock-up of the Helium-Cooled Pebble Bed (HCPB) breeder test blanket module (TBM) has been analysed on the basis of neutron transport, sensitivity and uncertainty calculations using both deterministic and probabilistic computational methods. The calculations revealed a slight but systematic underestimation of the measured tritium activities by 5 to 10% on average, independent of the nuclear data used that were taken from the EFF-3 and FENDL-2.0, -2.1 data files. The uncertainty assessments showed data related uncertainties of the calculated tritium production rates at a level of 4% (2σ confidence level). The beryllium cross-section data were shown to be the main source of these uncertainties. The total uncertainties of the tritium production prediction including the data uncertainties, the statistical uncertainties of the Monte Carlo calculation and the experimental uncertainties are in the order of 8 to 10% (2σ). The observed underestimation of the measured tritium production is at the lower bound of the assessed uncertainty margin. The obtained results indicate that design calculations for the tritium breeding ratio (TBR) of fusion power reactors employing a HCPB type breeder blanket are conservative. Thus, an additional TBR margin is provided which allows compensation for potential other uncertainties.

We present an overview of ongoing work on three types of neutron flux monitors under investigation and development for the two European ITER Test Blanket Modules: 1) a neutron activation system, 2) silicon carbide diodes, 3) self-powered neutron detectors for fast neutrons. A pneumatic test system for neutronics tests for a TBM-NAS was constructed at the DT neutron generator laboratory of Technical University of Dresden. Several irradiations have been performed with focus on the simultaneous measurement of the extracted activated probes. Furthermore, an engineering assessment in the conceptual design phase has been done which considered issues of design requirements and integration. Within the I-SMART project, KIT is investigating the suitability of an online detector based on silicon carbide semiconductor material and associated electronics for the TBMs. Detectors of several designs have been already irradiated with DT neutrons. Irradiation tests at elevated temperatures have been done and further tests are currently underway. Self-powered neutron detectors (SPND) with novel materials sensitive also to the fast neutron flux expected in the TBMs are under investigation. Simulations with the European Activation System EASY and neutron flux spectra which were calculated with MCNP for the HCPB TBM. Preliminary tests with commercial SPND in a fast reactor were performed. Test detectors are under preparation for testing with DT neutron generators. © 2015 IEEE.

Measurements of C12 cross sections for the excited states (n,p0) up to (n,p4) and (n,d0), (n,d1) have been carried out. The Van de Graaff neutron generator of the EC-JRC-IRMM laboratory has been used for these measurements. A very thin tritiated target (263 μg/cm2) was employed with deuteron beams energies impinging on the target in the range 2.5-4.0 MeV. Neutrons in the range 18.9-20.7 MeV were produced with an intrinsic energy spread of 0.2-0.25% FWHM. With such narrow neutron energy spread, using a high energy resolution device such as a single crystal diamond detector, several peaks from the outgoing charged particles produced by the (n,pn), (n,dn) and also (n,α0) reactions appear in the pulse height spectrum. The peaks can be identified using the reaction Q-values. The diamond detector used for these measurements has shown an intrinsic energy resolution lower than 0.9% FWHM. The analysis of the peaks has permitted to derive the partial carbon reaction cross sections for several excited states. The results are presented in this paper with the associated uncertainties and they are compared with different versions of TENDL compilation when these data are available (e.g. versions 2009, 2010, 2011 and 2015) and also with experimental results available in the EXFOR database. © The Authors, published by EDP Sciences, 2017.

A neutronics benchmark experiment on a pure Copper block (dimensions 60 × 70 × 70 cm3) aimed at testing and validating the recent nuclear data libraries for fusion applications was performed in the frame of the European Fusion Program at the 14 MeV ENEA Frascati Neutron Generator (FNG). Reaction rates, neutron flux spectra and doses were measured using different experimental techniques (e.g. activation foils techniques, NE213 scintillator and thermoluminescent detectors). This paper first summarizes the analyses of the experiment carried-out using the MCNP5 Monte Carlo code and the European JEFF-3.2 library. Large discrepancies between calculation (C) and experiment (E) were found for the reaction rates both in the high and low neutron energy range. The analysis was complemented by sensitivity/uncertainty analyses (S/U) using the deterministic and Monte Carlo SUSD3D and MCSEN codes, respectively. The S/U analyses enabled to identify the cross sections and energy ranges which are mostly affecting the calculated responses. The largest discrepancy among the C/E values was observed for the thermal (capture) reactions indicating severe deficiencies in the 63,65Cu capture and elastic cross sections at lower rather than at high energy. Deterministic and MC codes produced similar results. The 14 MeV copper experiment and its analysis thus calls for a revision of the JEFF-3.2 copper cross section and covariance data evaluation. A new analysis of the experiment was performed with the MCNP5 code using the revised JEFF-3.3-T2 library released by NEA and a new, not yet distributed, revised JEFF-3.2 Cu evaluation produced by KIT. A noticeable improvement of the C/E results was obtained with both new libraries. © The Authors, published by EDP Sciences, 2017.

The need for studies of the activation of materials in the neutron fluxes encountered in D-T fusion devices has long been recognized as a key area of fusion technology programs. In this paper a comparison between experimental and numerical results of the induced radioactivity in a low activation material, the SiC/SiC fiber ceramic composite, is presented. The SiC/SiC fiber ceramic composite is a candidate material for the DEMO phase of a commercial fusion power station. This material was exposed to the neutron flux produced by a D-T neutron generator and the induced activity was carefully measured using the Low Background Counting Facility in the Gran Sasso laboratory. The neutron flux and spectra at the irradiation position have been determined using foil activation and numerical calculations with the Monte Carlo Code MCNP. These quantities have been used as input values for the activation code FISPACT and the cross section library EAF 4.1, to calculate the induced activity. The material composition and its impurities have been taken from existing data. The results of the comparison are discussed, focusing on the validation of the cross sections and the activity coming from the impurities.